The present invention relates generally to an illumination and imaging system for a document reproduction device and, more particularly, to an efficient full frame light source and lens assembly.
Prior art full frame document illumination and imaging systems generally employ a flash lamp or series of flash lamps combined with a projection lens to provide full frame exposure of a document at a photosensitive image plane. Representative systems are disclosed in U.S. Pat. Nos. 3,697,177 (Booth) and 4,333,723 (Green et al). These prior art systems offer relatively high throughput compared to the conventional scan/rescan systems but also have several disadvantages. The flash lamps and their power supplies and quench circuits add a significant expense to the imaging system. And, typically, a large enclosed housing with reflective interior surfaces is required to enhance efficiency, adding to the system cost.
The flash lamps used in these prior art systems are all located out of the optical path; light reaches the platen by reflection from mirrors; directly from the lamps; or indirectly from reflectors associated with the lamps. The light undergoes multiple reflections from the interior reflective walls of the illumination housing. A generally uniform level of illumination is required at the document object plane which is a transparent platen in a typical reproduction device. This uniform illumination level, in practice, has proven difficult to achieve.
Another type of full frame illumination device is disclosed in copending U.S. Applications (D/84077 and D/84063). Both applications are assigned to the same assignee as the present invention. In the first mentioned application, a full frame illumination source is realized by forming a two-dimensional array of discrete light sources in the body of a transparent substrate. The substrate has dimensions corresponding to the document sizes to be reproduced and is positioned between the document and a projection lens, either conventional, or full-frame. The light sources, when energized, provide the required illumination level at the document/platen interface. In the second application, a transparent document platen is modified so that light introduced into the platen from an outside source is directed to the document/platen interface by total internal reflection thereby providing the document illumination.
The present invention is directed to a more efficient and novel mechanism for providing a full frame illumination and imaging system. A document platen is modified so that the edges are ground and made diffusely reflective to incident light. A platen extension is attached to the bottom of the platen, the extension also having diffusely reflective sides. A full frame lens array, having reflective interstitial lenslet areas forms the bottom surface of the assembly. Light is introduced into either the platen and/or platen extension area. The entire platen/platen extension/lens array acts as an integrating cavity efficiently directing and redirecting the light so as to uniformly illuminate the document. The reflected light image is then projected by the lens array onto a flat photoreceptor surface.
More particularly, the invention relates to an illumination and imaging system for illuminating a document and for transmitting an image of said document onto a photosensitive surface, said illumination and imaging system comprising:
a generally transparent platen having diffusely reflective side surfaces for supporting the document to be reproduced, PA1 a light housing connected to the bottom of said platen in a light-tight manner, said housing having diffusely reflective interior side surfaces, PA1 a two-dimensional, full frame lens array connected to the bottom of said light housing in a light-tight manner, said lens array comprising a plurality of individual lenslets separated by opaque insulating material, the top surface of said lens array partially covered by a reflective layer formed between the lenslet interstitial array, and PA1 means for coupling illumination into the light housing, said illumination being diffusely reflected from said platen and light housing sides and from the interstitial lenslet area and document to provide a generally uniform level of illumination at the platen/document interface, a reflected image of the document being projected through the lens array onto the photosensitive surface.